Threadless fans: If there’s a T-shirt design you’ve been coveting, this week’s the good time to buy. Starting today through 10 a.m. on Monday, April 27, Threadless is donating $1 per order to plant trees.

$1 seems like a pretty nice commitment — especially considering the fact that many Threadless T-shirts cost just $9. While the winning designs from the recent Threadless Loves Green contest — priced between $15 - $25 — are the ones featured on the front page, many eco-conscious designs can be yours for just $9. Some of my faves:

From left to right, those are Fossil Fuel, We are Made of Carbon and Maple Walnut. Lots more cute eco-designs are also available, so browse the $9 sale pages. Some, but not all, shirts are made of organic cotton, so choose wisely.

Don’t need any more T-shirts, but still want to plant a tree? Swaptree’s running a “Swap for Free and Plant a Tree” dealio for Earth Day. Just swap what you’ve already got for something someone else has already got — whether it’s books, DVDs, CDs, or video games — on April 22. Swaptree will then plant a tree for you free; the company hopes to plant 10,000 trees through the initiative.

Both Threadless and Swaptree’s trees will be planted through Plant A Billion Trees

, a Nature Conservancy initiative. For every swap done on Swaptree on Earth Day, 4/22, Swaptree will plant a tree. They are working with,, which is a Nature Conservancy initiative.

Images: Courtesy